The aims for the next year's research are threefold: 1. We plan to separate IgD ion and IgD- spleen cells of adult mice with aid of the cell sorter and assess their reactivity in the Mishell-Dutton culture. The expectation is that they will behave like CR ions and CR- cells. 2. We would like to address the issue of differentiation of CR-cells. These cells differentiate under the influence of Interleukin 1 to CR ion IgD ion cells which are thought to represent the precursors of antibody forming cells. Experiments will be designed to induce differentiation in CR- cells, then separate the generated IgD ion and IgD- cells and test separately their ability to form antibody. 3. PC.2 is a new plasma cell antigen defined by monoclonal antibodies. We will investigate the association of this antigen with cells in transition from resting B lymphocytes (e.g. IgD ion cells ) to antibody forming cells.